In a mobile wireless communication system, a channel is not constant between a transmitter and a receiver. Thus, it is necessary to often measure the channel between a transmission antenna and a reception antenna. When a predefined signal is transmitted and received to measure the channel, the receiver may determine the amplitude decrease and phase shift of the channel using the predefined signal and may feed back the determined information to the transmitter. In addition, the receiver may detect and decode data information reliably based on the determined information. The signal predefined between the transmitter and the receiver may be referred to as a reference signal, a pilot signal, or an SRS.
In the present 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) system, a UE with two or more antennas uses a single power amplifier and thus has difficulty in simultaneously transmitting an SRS through two or more antennas. In contrast, a power amplifier is available for each antenna in an LTE-Advanced (LTE-A) system. Accordingly, there exists a need for studying a method for simultaneously transmitting an SRS through two or more antennas.
FIG. 1 illustrates an example in which a UE with two antennas transmits an SRS.
In FIG. 1, the horizontal axis represents frequency and the vertical axis represents time. ‘n_SRS’ is the index of a time when an SRS is transmitted. Only Orthogonal Frequency Division Multiple Access (OFDMA) symbols carrying SRSs are shown from among OFDMA symbols contiguous in time in FIG. 1, for the convenience's sake of description. For example, other OFDMA symbols may be interposed between OFDMA symbols with index n_SRS=0 and index n_SRS=1, while not shown in FIG. 1.
In FIG. 1, ‘Axy’ (x=0, 1 and y=0, 1) denotes a Resource Block (RB) allocated to a particular antenna, antenna y of a particular UE, UE x, for transmitting an SRS. Herein, x is the identification number of a UE and y is the identification number of an antenna in each UE. For example, ‘A0y’ denotes an RB allocated to antenna y of UE 0, and ‘A1y’ denotes an RB allocated to antenna y of UE 1. In addition, ‘Ax0’ denotes an RB allocated to antenna 0 of UE x and ‘Ax1’ denotes an RB allocated to antenna 1 of UE x. Thus, ‘A01’ denotes an RB allocated to antenna 1 of UE 0.
Referring to FIG. 1, RBs are not allocated simultaneously to antenna 0 and antenna 1 of UE 0. That is, an SRS is not transmitted simultaneously through antenna 0 and antenna 1. For example, RB A00 is allocated to time positions n_SRS=0, 2, 4, and 6 for antenna 0 of UE 0, whereas RB A01 is allocated to time positions n_SRS=1, 3, 5, and 7 for antenna 1 of UE 0. Likewise, RBs are not allocated simultaneously to antenna 0 and antenna 1 of UE 1. That is, Each UE may transmit an SRS using two antennas alternately between time areas, with frequency hopping, as illustrated in FIG. 1.